So before you start building your vault, a few points to keep in mind:

1. First of all, calm down.

2. There is still no compelling reason to believe that this strain, influenza A(H1N1)1, is significantly more virulent than a typical seasonal influenza.

Your run-of-the-mill flu season has a case-fatality ratio of very roughly 0.1%, or 32% of hospitalizations [1]. Let’s narrow that to the 19-to-64 demographic, which could be most susceptible to this current outbreak (an unusual pattern seen in pandemic flus and likely caused by an overly robust immune response in healthy adults [2]), and is least susceptible to the seasonal flu. Within that population, CFR is about 0.03%, or 7% of hospitalizations [1]. Past influenza pandemics have had CFRs of anywhere from 0.1% in the 1957 and 1968 outbreaks to 2.5%2 in the 1918 “Spanish flu” [3].

In contrast, the CFR in the case of influenza A(H1N1) could be anywhere from 3.1% (an upper bound, based on a maximum of 8 laboratory-confirmed influenza A(H1N1) deaths out of a minimum of 257 laboratory-confirmed influenza A(H1N1) cases worldwide, from WHO figures available at time of writing) to 0.0016% (a very conservative lower bound, based on an approximate hospitalization rate of 0.4% of all cases in the 19-64 demographic in a typical flu season [1], with which an attack rate was extrapolated from 2000 estimated hospitalizations in Mexico).

Using figures that are quitepopular in the press gives a CFR of about 7.5% in Mexico (some 150 deaths in 2000 hospitalizations, the latter very dubiously assumed to be equal to the number of cases). Because of the unreliability of the “suspected” case count in Mexico, I am not convinced that this particular CFR estimate is useful at all, even as an upper bound. It’s far more likely that the actual CFR falls somewhere between 0.0016% and 3.1%.

All of these numbers don’t tell us very much (except that it is highly unlikely that this is some epic killer virus), but that’s exactly the point. Just because (thanks in large part to the surveillance infrastructure put into place in the wake of the “avian flu” panic) this (potential) pandemic has been spotted, there is no reason to assume that we have any solid evidence suggesting that the virulence of this pathogen is particularly high. However, this may very well change as time goes on and as the situation becomes clearer, and it certainly does not mean that the virus is not dangerous.

3. Virulence is not the same as pathogenicity. Perhaps more precisely, the concepts are not the same, though the terms may often become scrambled in the fray. The salient point is that while influenza A(H1N1) has proven highly pathogenic (i.e. it is highly infectious and spreads rapidly), there is not much evidence to suggest that it is especially virulent (i.e. it has not been associated with unusually high mortality or morbidity). So while governments everywhere are preparing for the possibility of a pandemic, the severity of the disease (to wit, the “causing serious illness” criterion from the linked WHO document) is far from clear at this point. And hopefully I was able to convince you in Point 2 that there is as yet no reason to suspect any greater virulence from this strain than a typical seasonal flu strain.

4. Influenza A(H1N1) has a few key differences to Severe Acute Respiratory Syndrome (SARS) and influenza A(H5N1) or “avian flu”. For one, both SARS and avian flu were much deadlier; the SARS outbreak in Hong Kong had a CFR of about 14-17% [4], while the avian flu has a CFR of something like 14-33% [3]. However, avian flu never demonstrated efficient human-to-human transmission, which made it a very deadly disease that was unlikely to spread quickly. Likewise, SARS has never been observed to be contagious before the onset of symptoms, which significantly increases the likelihood that a person at risk of transmitting SARS can be identified by basic surveillance. Influenza A(H1N1), while appearing (for now) to be far less virulent than either of these two recent serious respiratory disease outbreaks, is also considerably more likely to spread rapidly and become pandemic.

A confirmed case of S-OIV infection is defined as a person with an acute febrile respiratory illness with laboratory confirmed S-OIV infection at CDC by one or more of the following tests:

real-time RT-PCR

viral culture

A probable case of S-OIV infection is defined as a person with an acute febrile respiratory illness who is positive for influenza A, but negative for H1 and H3 by influenza RT-PCR

A suspected case of S-OIV infection is defined as a person with acute febrile respiratory illness with onset

within 7 days of close contact with a person who is a confirmed case of S-OIV infection, or

within 7 days of travel to community either within the United States or internationally where there are one or more confirmed cases of S-OIV infection, or

resides in a community where there are one or more confirmed cases of S-OIV infection.

You can make of that what you will. It seems to me that there is probably no logistical barrier preventing health care entities other than the CDC from confirming the influenza A(H1N1) subtype, except for one reason or another it doesn’t count as “confirmed” unless the CDC does it.

6. When I first began considering and looking into the actual severity of the whole “swine flu” panic, I thought exactly the same thing that Obama said earlier this week: this flu outbreak (and likely pandemic) is, based on the information we currently have, a cause for concern but not alarm.

If there is one good thing that has come out of what is arguably a gross overreaction by the American media, it is a heightened awareness of the importance of public health and good hygiene. So remember kids, listen to the President and wash your hands.

1I have used the nomenclature preferred by the World Health Organization as of 30 April 2009.

2The 2.5% CFR figure for the 1918 pandemic, though almost canonical, seems highly questionable given the estimates of 20-100 million deaths at a time when the world had a population under 2 billion. In any case, data from that pandemic are likely iffy at best.

Let us not wallow in the valley of despair. I say to you today, my friends, that in spite of the difficulties and frustrations of the moment, I still have a dream. It is a dream deeply rooted in the American dream. I have a dream that one day this nation will rise up and live out the true meaning of its creed: “We hold these truths to be self-evident: that all men are created equal.” I have a dream that one day on the red hills of Georgia the sons of former slaves and the sons of former slaveowners will be able to sit down together at a table of brotherhood. I have a dream that one day even the state of Mississippi, a state, sweltering with the heat of injustice, sweltering with the heat of oppression, will be transformed into an oasis of freedom and justice. I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character. I have a dream today.

At around 0720 GMT, a bomb was detonated in Baghdad’s al-Ghazl animal market. 20 minutes later, a bomb was set off in another crowded market in the al-Jadida district, southeast of Baghdad. The figures below are accurate as of the posting of this entry.

The BBC reports that the first explosion killed at least 46 and injured another 80, and that the second explosion killed at least 27 and injuring 67. That adds up to at least 73 dead, 147 wounded.

CNN reports that the first killed 69 and injured more than 140, and that the second killed 29 and injured 67. The sum is 98 dead, and at least 207 wounded.

Al Jazeera English reports that the first bomb killed 38 and the second at least 27. They estimate about 149 injured total. That is at least 65 dead, 149 wounded.

U.S. officials, according to CNN, reported a dramatically lower death toll: 27 dead and 53 wounded.

This is all very interesting, but whatever. The most interesting difference between the reports is that the BBC and CNN stories refer to Qassem Ata al-Moussawi (and any number of alternate spellings), “a spokesman for Baghdad’s security plan,” (what does that mean, anyway?) stating that the bombers, both women, were likely mentally disabled and the bombs detonated remotely. Both of them incorporated this prominently into their stories and headlines.

However, neither the Al Jazeera story nor the U.S. military make any mentions of the women’s mental states. The NY Times article vaguely mentions Iraqi officials’ comments about the women potentially being mentally disabled, but essentially disregards it, noting that “…Iraqi officials have made similar claims in the past….”